Unwanted mail (e.g., spam, junk mail, etc.) is classified as gray mail. Gray mail by definition is mail that users disagree on whether they would like to receive or not receive. As an example, some users may consider frequent sales communication from a certain store as spam while others may want to receive these mailings. To assist user's avoid gray mail, several web-based email services expose an unsubscribe user interface (UI) upon detecting a list-unsubscribe header in the email. The UI allows the user to automatically generate an unsubscribe request to the sender rather than having to search through the email itself to locate the unsubscribe request contained in the body of the email message. However, some senders may not honor an unsubscribe request submitted by a user and hence diminish the user trust in the unsubscribe feature.
Because of this, many users select the “report spam” button as an alternative to using the unsubscribe link UI provided by their email service. Users may also prefer to select the “report spam” button because they believe that using the unsubscribe link UI confirms the existence of an email address with an active user behind it, leading to more “spam.” Another reason a user may select the button is an inability to find the unsubscribe link. Senders often bury the unsubscribe link towards the end of the email message.
Selecting a “report spam” button also does not solve all of the user's problems. A user often receives the same unwanted email message over and over again despite reporting it as spam. The spam block feature of the user's email account cannot add every sender reported by the user to the user's block-list for several reasons. First, block-lists could get full very fast as spammers very easily can change their FROM: address. Second, false positives (unintentionally blocking a sender) associated with users sometimes abusing the button or not liking the content of the specific mail but still wanting to receive future mailings from that sender.